Retrospective study of the functional and oncological outcomes of conformal sphincter preservation operation in the treatment of very low rectal cancer

This retrospective study was conducted in the Department of Colorectal Surgery, Changhai Hospital, Shanghai, China. All procedures were performed in accordance with the ethical standards of our institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The demographic, clinicopathological and follow-up information were recorded in our Colorectal Cancer Database. All patients who had CSPO performed by the same surgical team between January 2011 and October 2018 were reviewed. Patients who met all of the following criteria were included into the study: (1) proven rectal adenocarcinoma with digital rectal examination, colonoscopy and biopsy; (2) the tumor did not infiltrate the intersphincteric space; (3) neoadjuvant therapy in the case of preoperative stage T3–T4 or N+ , or if the circumferential margin was considered positive; (4) good anal function before the operation; (5) the distance from the inferior tumor edge to the anal verge was less than 4–5 cm on rectal digital examination; or less than 2 cm from the dentate line on proctoscopy or colonoscopy; (6) the diameter of the tumor was less than 3 cm and occupied less than 1/3 circumference of the lumen (the actual diameter measured after resection may be slightly larger). Exclusion criteria were: (1) distant metastasis including those with metastatic lymph nodes outside of mesorectum; (2) poorly differentiated or undifferentiated cancers; (3) patient unable to tolerate the operation (American Society of Anesthesiologists (ASA) class > 3).

The CSPO starts with standard mobilization of the sigmoid colon, ligation of the inferior mesenteric artery at its origin and mobilization of the rectum according to the principle of total mesorectal excision (TME) with attention paid to preserve the autonomic nerves. Dissection of the rectum continues downward until reaching the hiatal ligament [11]. After cutting the hiatal ligament (Fig. 1), dissection stops at the entrance of the intersphincteric space, which is one of the main differences between ISR and CSPO (Fig. 2). The rectum is transected at the rectosigmoid junction. Subsequently, the anus is dilated to 3–4 fingers wide and the rectum was pulled out of the anus through the rectal lumen (Fig. 1). The conformal incision line is designed according to the tumor’s location and size. The key point of this procedure is to preserve as much of the lower rectum, dentate line and internal anal sphincter, on the side opposite to the tumor as possible. The intersphincteric space was left undisturbed to prevent injuring the numerous nerve fibres it contains [7] to preserve the function of the remaining internal sphincter. The distal dissection line is made at least 1 cm below the inferior tumor margin under direct vision. In cases where the tumor cannot be inverted from the rectum, in-situ transanal excision can still be performed to preserve adequate rectal wall appropriately. The remnant rectal stump was then closed with interrupted sutures. Intraoperative frozen-section examination was performed in all cases to ensure an adequate oncological DRM. Following the rectal stump closure, a 25 mm circular stapler (CDH25, Johnson & Johnson, USA) was used to perform the anastomosis [12] (Fig. 1). The stapler is inserted as high in the rectal stump as possible, to make the anastomosis as high as possible on the opposite side. Consequently, as much as possible of the dentate line and internal anal sphincter are preserved on the opposite side. Temporary ileostomy was routinely performed in all patients. The anastomotic line is shown in Fig. 3: it is 2–3 cm above the dentate line even though the patient has such a low rectal cancer. Patients with pathological stage III or stage II disease with high-risk features received postoperative Capeox or mFOLFOX6 regimen as adjuvant chemotherapy. Postoperative radiotherapy was performed in patients who had not had preoperative radiotherapy according to the following criteria: (1) pathological result ≥ N1b or circumferential resection margin (CRM) positive; (2) T3 or T4; (3) distal margin too short (usually less than 0.3 cm).

The ileostomy was closed 3–6 months after the resection or after finishing adjuvant chemical or chemo-radio therapy, depending on the clinical fitness of the patient and the following criteria: (1) the digital rectal examination was performed every 4 weeks after the resection to make sure the anastomotic ring was smooth, complete and no stenosis; (2) local recurrence excluded by pelvic magnetic resonance imaging (MRI), a chest computed tomography (CT) scan and MRI of liver excluded distant metastases; (3) defecography with iodized water was performed when there was any suspicion of an anastomotic leakage; (4) colonoscopy was performed to make sure that there was no stenosis and local recurrence at the anastomosis and that the anastomotic line was complete and with no obstruction in the proximal bowel.

Patients were followed every 3 months for the first 2 years, every 6 months for the next 3 years, and once a year thereafter. Digital rectal examination, carcinoembryonic antigen and carbohydrate antigen 19-9 test were performed at every follow-up visit; chest CT scan, MRI of the liver and pelvis with intravenous contrast and colonoscopy was performed according to the National Comprehensive Cancer Network (NCCN) guidelines. Postoperative complications were graded according to the Clavien–Dindo classification system [13]. Anal function was assessed 12 months after ileostomy closure using the Wexner fecal incontinence and low anterior resection syndrome (LARS) score [14, 15].

The continuous variables were reported as mean ± standard deviation (SD) or as median with interquartile ranges (IQR), depending on whether the data were normally distributed or not. Categorical variables were statistically analyzed by the Chi-square test and continuous variables were compared using Student’s t test or Mann–Whitney test. The baseline characteristics and follow-up results were compared between the patients with and without neoadjuvant chemoradiotherapy (nCRT). The Kaplan–Meier method and log rank test were used for analysis of prognostic factors for disease-free survival, overall survival and stoma-free survival. A p value < 0.05 (two sided) was considered statistically significant. Statistical analysis was performed using IBM SPSS Statistics 23.0 (IBM SPSS Statistics, IBM Corporation, Armonk, NY, USA). Figures were generated using GraphPad Prism 7.02 (GraphPad Software Inc., La Jolla, CA, USA).

A total of 102 patients (mean age 56.9 ± 10.8 years) met the inclusion criteria and had CSPO between January 2011 and October 2018. The mean body mass index was 23.0 ± 3.3. A total of 35 patients (34.3%) received nCRT followed by resection 6–8 weeks after the completion of the neoadjuvant therapy. The other 67 patients (65.7%) were treated by surgery without neoadjuvant treatment. Seventeen patients (16.7%) received postoperative radiotherapy. The approach was by laparoscopy in 38 patients (37.3%), including 1 (2.6%) conversions to open surgery, and 64 (62.7%) were open procedures. The median tumor distance from the anal verge was 3 (IQR, 3–4) cm.

The colorectal (or coloanal) anastomoses were performed with stapling except in one case when the tumor was too low for a stapled anastomosis and a hand-sewn anastomosis was performed. One planned CSPO was converted to APR, because two consecutive intraoperative frozen-section examinations showed tumor cells at the resection margin, despite absence of visible tumor. The median DRM was 0.5 (IQR, 0.3–0.8) cm and all patients had R0 resection and negative CRM, except one patient who had a positive DRM (< 1 mm). The median number of lymph nodes retrieved was 14 (IQR, 10–15.25) and the median tumor diameter was 2.7 (IQR, 2–3.5) cm. Complete pathological response to neoadjuvant therapy was achieved in 7 of the 35 patients who received nCRT (20.0%). Comparing the nCRT and non-nCRT group, age was significantly lower, the tumor’s largest diameter was significantly smaller and cT stage and cN stage were more advanced in the nCRT group (Table 1).

There was no 30-day mortality. The overall complication rate was 19.6%. According to the Clavien–Dindo classification [13], overall incidence of grade 2 or higher postoperative complications was 14.7% (15/102). The details of complications in both groups are reported in Table 2.

The median duration of follow-up was 28 (IQR, 12–35) months. The disease-free survival rates at 1, 2 and 3 years were 92.5%, 86.3% and 83%, respectively (Fig. 4). The 3-year local recurrence-free and distant recurrence-free survival rates were 97.5% and 86%, respectively. The local recurrence rate was 2% and the distant metastasis rate was 10.8%.

The ileostomy was reversed in 79 patients (77.5%; Fig. 5) with a median time to reversal of 7 (IQR, 4–10) months. The rates of ileostomy reversal in the nCRT and non-nCRT groups was 71.4% (25/35) and 80.6% (54/67), respectively, however, the difference was not statistically significant (p = 0.29). The median time to ileostomy reversal for nCRT and non-nCRT patients was 8 (IQR, 5.0–9.5) and 7 (IQR, 4–10) months, respectively. However, the difference was not statistically significant (p = 0.72). The ileostomy-free survival is shown in Fig. 6.

The mean Wexner incontinence and LARS score were 5.9 ± 4.3, and 29.2 ± 6.9. A total of five patients (11.4%) had no LARS (score 0–20), 18 (40.9%) minor LARS (score 21–29), 21 (47.7%) major LARS (score 30–42). The mean Wexner score with or without nCRT was 7.1 ± 5.0 and 5.3 ± 4.0, respectively (p = 0.15). The mean LARS score with or without nCRT was 31.4 ± 6.4 and 28.4 ± 6.9 (p = 0.19). For the postoperative radiotherapy patients, the mean Wexner score was 7.3 ± 4.1 (p = 0.92, in comparison to nCRT patients), the mean LARS score was 29.6 ± 1.9 (p = 0.47, in comparison to nCRT patients), 12 months after ileostomy reversal.